In dealing with the transferring of liquid metals from a furnace by means of a crucible or ladle, there are a number of potential difficulties. One common type of problem deals with handling of certain metals, particularly non-ferrous metals such as aluminum. Molten aluminum is very reactive chemically and therefore very corrosive to metal containers. To combat this problem metal containers or crucibles are occasionally replaced by ceramic or refractory formed or lined components. The difficulty that occurs with this type of structure is that ceramic or refractory components are brittle and easily broken upon impact. Also, some are subject to thermal shock and when they are used with metal, allowance must be provided for low thermal expansion. Accordingly, it is desirable where possible to use metal crucibles or ladles to handle, transport and meter liquid metals. In fact, one type of successful crucible for this purpose is depicted and described in U.S. Pat. No. 4,073,414. The type of structure in that reference has proved to be extremely valuable and useful in overcoming many problems in the liquid metal handling field.
Further improvements are desirable particularly when working with molten metals such as aluminum. Carbon bonded silicon carbide products have been used for melting, holding and pouring crucibles, thermocouple protection tubes, pressure pouring tubes, launders and other devices for handling molten metal, especially non-ferrous alloys. To date, bottom pouring carbon bonded silicon carbide crucible has not been successfully manufactured. The main problem has been sealing the bottom orifice. The extremely hard and coarse silicon carbide grains make the products difficult to machine, especially to cut threaded portions that will be continuous and smooth enough to hold molten metal.